ML070360253

of Regulatory Guide 1.76, Design-Basis Tornado and Tornado Missiles for Nuclear Power Plants (Formerly Draft Regulatory Guide DG-1143)

ML070360253
Person / Time
Issue date:	03/12/2007
From:	Harvey B NRC/NRO/DSER/RSAC, Office of Nuclear Regulatory Research
To:
Harvey Brad, NRO/DSER/RSAC, 415-4118
Shared Package
ML070260280	List: ML070360253
References
DG-1143, FOIA/PA-2015-0456, FOIA/PA-2015-0458 RG-1.076, Rev 1
Download: ML070360253 (12)

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T h e U.S. N u c le a r R e g u la to ry C o m m is s io n (N R C) i s s u e s re g u la to ry g u id e s to d e s c rib e a n d m a k e a v a il a b le to th e p u b li c m e th o d s th a t t h e N R C s ta ff con si der s acc ept abl e f or us e i n i m pl em ent i ng spe ci f i c par t s of t he age ncy's r egu l at i ons , t ech ni que s t hat t he st af f us es i n e val uat i ng spe ci f i c pr obl em s or po st ul at ed acc i den t s, an d d at a t hat t he st af f ne ed i n r evi ewi ng app l i cat i ons f or pe r m i t s and l i cen ses. Regul at or y gu i des ar e n ot s ubs t i t ut es f or r egu l at i ons , an d c om pl i anc e wi t h t hem i s not r equ i r ed. Met hod s and s ol ut i ons t hat di f f er f r om t hos e s et f or t h i n r egu l at or y gu i des wi l l be de em ed acc ept abl e i f t hey pr ovi de a b asi s f or t he f i ndi ngs r equ i r ed f or t he i ss uan ce or c ont i nua nce of a per m i t or l i cen se by t he C om m i ss i on.T hi s gui de was i ss ued af t er c ons i der at i on of c om m ent s r ece i ved f r om t he pub l i c. The N R C s t af f en cou r age s and wel com es com m ent s and s ugg est i ons in c o n n e c ti o n w it h i m p ro v e m e n ts to p u b li s h e d re g u la to ry g u id e s , a s w e ll a s i te m s fo r i n c lu s io n i n re g u la to ry g u id e s th a t a re c u rre n tl y b e in g d e v e lo p e d. T h e N R C s ta ff w il l re v is e e xis ti n g g u id e s , a s a p p ro p ria te , t o a c c o m m o d a te c o m m e n ts a n d to re fl e c t n e w i n fo rm a ti o n o r e xp e rie n c e. W rit te n c o m m e n ts m ay be s ubm i t t ed t o t he R ul es and D i r ect i ves Br anc h, O f f i ce of Adm i ni st r at i on, U.S. N ucl ear R egu l at or y C om m i ss i on, W ash i ngt on, D C 20 555-000 1.R egul at or y gui des ar e i ssued i n 10 br oad di vi si ons: 1, P ow er R eact or s; 2, R esear ch and T est R eact or s; 3, Fuel s and M at er i al s Faci l i t i es;4, Env i r on m en t al a nd Si t i ng; 5 , Ma t er i al s a nd Pl an t Pr ot ec t i on; 6 , Pr od uc t s; 7 , Tr an s po r t at i on; 8 , Occ up at i on al Hea l t h; 9 , Ant i t r us t a nd F i na nc i al Rev i ew;a n d 1 0 , G e n e ra l.R equ est s f or s i ngl e c opi es of dr af t or ac t i ve r egu l at or y gu i des (whi ch m ay be r epr odu ced) s hou l d b e m ade t o t he U.S. N ucl ear R egu l at or y C om m i ss i on, W ash i ngt on, D C 20 555 , At t ent i on: R epr odu ct i on and D i st r i but i on S er vi ces Sect i on, or by f ax t o (301) 41 5-228 9; or by em ai l t o D i st r i but i on@nr c.gov. E l ect r oni c cop i es of t hi s gui de and ot her r ece nt l y i ss ued gu i des ar e a vai l abl e t hr oug h t he N R C's pub l i c W eb si t e u nde r t he R egu l at or y G ui des do cum ent c o ll e c ti o n o f t h e N R C's E le c tro n ic R e a d in g R o o m a t ht t p://w w w.nr c.gov/r eadi ng-r m/doc-col l ect i ons/ a n d th ro u g h th e N R C's A g e n c yw id e D o c u m e n ts A c c e s s a n d M a n a g e m e n t S ys te m (A D A M S) a t h ttp://w w w.n rc.g o v/re a d in g-rm/a d a m s.h tm l, un der Acces si on N o. ML0703 602 53.U.S. N UC LEA R RE GU LA TO RY C OM MI SSIO N M ar ch 2007 R ev i si on 1 RE GUL AT ORY GUI DE OFFICE OF NUCL EA R REGULA TORY RESEA RCH R E G U LA TO R Y G U I D E 1.76 (D r af t w as i ssued as DG-1143, dat ed Ja nuar y 200 6)DESI GN-BA SI S T ORNA DO A ND T ORNA DO M I SSI L ES FO R N U C LE A R P O W E R P LA N TS A. INT ROD UC TIONThi s re g ul at or y g ui de p ro v id es li ce ns ee s an d ap pl ic an ts w it h ne w g ui da nc e th at th e st af f of the U.S. N uclear Reg ulatory C om m ission (NR C) consid ers acc eptable for us e in selecting the d esig n-basis tornado and des ig n-basis tornado-g enerated m issiles tha t a n uclear pow er plan t sho uld b e desig ned to w ithstand to pre v ent u ndue risk to the h ealth a nd safety of the p ublic. This g uidanc e ap plies to th e co nt ig uo us U ni te d S ta te s, w hi ch is d iv id ed in to th re e re g io ns; t hi s do cu m en t p ro v id es s ep ar at e g uidanc e for each reg ion.This g uide does not a ddress the d eterm ination of the des ig n-basis tornado and torna do m issiles for sites located in A lask a, Haw aii, o r Pu erto R ico; the N RC w ill ev aluate such determ inations on a c as e-by-ca se b as is. Th is g ui de a ls o do es n ot id en ti fy th e sp ec if ic s tr uc tu re s, s y st em s, a nd c om po ne nt s that sh ould be d esig ned to w ithstand the effe cts of the d esig n-basis tornado or shou ld be pro tected from torna do-g enerated m issiles an d rem ain fu nctiona l. This g uide also d oes not a ddress extrem e w inds, such as h urricanes , o r the m issiles attribu ted to suc h w inds. Tornad o w ind s peeds m ay no t bou nd hurrican e w ind s peeds for certain portion s of the A tlantic an d G ulf co asts, at the wind spe ed freq uencies of o ccurrenc e co nsidered in this g uide. The NR C will a ddress these extrem e co nditions on a case-by-case basis. This g uide also d oes not a ddress other externally g enerated haz ards s uch as av iation c rashes, nearby accid ental e xplosio ns res ulting in blast o v er-pressure lev els an d ex plosion-borne deb ris and m issiles, and turbine m issiles.

Rev. 1 of RG 1.76, Pa g e 2Gen eral D esig n C riterion (G DC) 2, "D esig n B ases fo r Pro tection Ag ainst N atural P heno m ena,"of A ppen dix A , "Gen eral D esig n C riteria for Nuc lear P owe r Plan ts," to Title 10, Pa rt 50, of the Cod e of F edera l Re gulation s (10 C FR Pa rt 50), "D om estic L icensing of Prod uction and Utiliz ation Facilities"(Ref. 1), requ ires that structures, sy stem s, and com pone nts th at are im portant to safe ty sha ll be desig ned to w it hs ta nd th e ef fe ct s of n at ur al p he no m en a, s uc h as to rn ad oe s, w it ho ut lo ss o f ca pa bi li ty to p er fo rm their safe ty fun ctions. G DC 2 also re quires that the des ig n b ases fo r these structu res, sy stem s, and com pone nts sh all reflect (1) ap propriate consid eration of the m ost se v ere o f the natural phen om ena th at h av e be en h is to ri ca ll y r ep or te d fo r th e si te a nd s ur ro un di ng a re a, w it h su ff ic ie nt m ar g in for the lim ited ac curacy , q uantity , a nd period of tim e in whic h the histo rical da ta hav e be en a ccum ulated, (2) ap pr op ri at e co m bi na ti on s of th e ef fe ct s of n or m al a nd a cc id en t c on di ti on s w it h th e ef fe ct s of the natu ral ph enom ena, and (3) the im portanc e of the sa fety fun ctions to be perfo rm ed.GD C 4, "Env ironm ental a nd Dy nam ic E ffects D esig n B ases," of App endix A to 10 C FR Pa rt 50 re qu ir es , in p ar t, th at s tr uc tu re s, s y st em s, a nd c om po ne nt s th at a re im po rt an t t o sa fe ty s ha ll b e ad eq ua te ly pr ot ec te d ag ai ns t t he e ff ec ts o f m is si le s re su lt in g f ro m e v en ts a nd c on di ti on s ou ts id e th e pl an t.For stationary po wer reactor site ap plications sub m itted be fore January 10 , 1 997, para g raph 100.10(c)(2) of 1 0 C FR Pa rt 100 , "Reac tor S ite C riteria" (R ef. 2), states th at m eteorolo g ical co nditions at th e si te a nd in th e su rr ou nd in g a re a sh ou ld b e co ns id er ed in d et er m in in g th e ac ce pt ab il it y o f a si te fo r a po w er r ea ct or.For stationary po wer reactor site ap plications sub m itted on or after January 10 , 1 997, para g raph 10 0.20 (c)(2) o f 10 C F R P ar t 1 00 r eq ui re s th at m et eo ro lo g ic al c ha ra ct er is ti cs o f th e si te th at a re n ec es sa ry for safe ty ana ly sis or m ay hav e an im pact u pon plant desig n (su ch a s m axim um pro bable wind spe ed)m ust b e co nsidered in determ ining the acceptab ility of a site for a nuclear pow er plan t. I n ad dition, parag raph 100.21(d) of 1 0 C FR Pa rt 100 requ ires that the p hy sical ch aracteristics of the site, inclu ding m eteorolo g y , m ust b e ev aluated and site pa ram eters es tablished suc h tha t pote ntial thre ats from suc h phy sical ch aracteristics will p ose no undu e risk to the ty pe o f facility pro posed to be lo cated at the site.Thi s re g ul at or y g ui de r el at es to in fo rm at io n co ll ec ti on s th at a re c ov er ed b y th e re qu ir em en ts of 1 0 C FR Pa rt 50, 10 C FR Pa rt 52, and 10 C FR Pa rt 100 , w hich the O ffice of Manag em ent an d B udg et (OMB) app rov ed u nder OMB con trol nu m bers 3 150-0011 , 3 150-0151 , a nd 3150-0093 , re spectiv ely. The NR C m ay neith er co nduc t nor spon sor, and a pe rson is no t requ ired to respo nd to, an in form ation co ll ec ti on r eq ue st o r re qu ir em en t u nl es s th e re qu es ti ng d oc um en t d is pl ay s a cu rr en tl y v al id O MB co nt ro l n um be r.B. DISC US SION Re gio nal iz at ion of To r nado Win d Spe e dsN uc le ar p ow er p la nt s m us t b e de si g ne d so th at th ey r em ai n in a s af e co nd it io n un de r se v er e m et eo ro lo g ic al e v en ts , in cl ud in g th os e th at c ou ld r es ul t i n th e m os t s ev er e to rn ad o th at c ou ld r ea so na bl y be p redicted to oc cur a t the site. The N RC bas ed th e orig inal v ersion of R eg ulatory G uide 1.7 6, publish ed in A pril 19 74, on WAS H-1300 (R ef. 3). WAS H-1300 cho se the des ig n-basis tornado wind spe eds so th at the proba bility that a torn ado exceed ing the desig n b asis w ould occur was on the o rder o f 10 p er y ea r pe r nu cl ea r po w er p la nt. WA S H-13 00 u se d on ly 2 y ea rs o f ob se rv ed to rn ad o in te ns it y d at a!7 (1 97 1 an d 19 72) to d er iv e th e co nd it io na l p ro ba bi li ty th at , if a to rn ad o w er e to s tr ik e a nu cl ea r po w er p la nt , the m axim um torna do wind spe ed w ould exceed a specified v alue. The pro bability that the to rnado wou ld strik e a nuclear pow er plan t (treated as a point) was based on m ore d ata.

Rev. 1 of RG 1.76, Pa g e 3The desig n-basis tornado w ind s peeds prese nted in this reg ulatory g uide are b ased on Rev ision 2 of N UR EG/CR-4461 (R ef. 4). The torn ado databas e us ed in that rev ision of N UR EG/CR-4461 inclu des i nf or mat i on re c or de d f or m or e th a n 4 6, 80 0 t or na do se gm e nt s oc c ur r i ng f r om J a nu a r y 1, 1 95 0, th r ou gh Au gus t 31 , 2 00 3. Mo r e th a n 3 9, 60 0 o f th os e se gm e nt s ha d s uf f i c i e nt in f or mat i on on th e i r lo c a t i on , i nt e ns i t y, leng th, and width to be u sed in the ana ly sis of tornado strik e pro babilities and m axim um w ind s peeds. Rev ision 2 o f N UR EG/CR-4461 differs from R ev ision 1 o f that report, w hich was publish ed in A pril 20 05. The s ec on d re v is io n of N U R E G/C R-44 61 r el ie s on th e E nh an ce d-F ujit a (E F) sc al e (R ef. 5) to r el at e the d eg ree o f dam ag e from a tornado to the to rnado m axim um w ind s peed. The earlier v ersions of the repo rt used the orig inal F uji ta scale. The m ethods use d in Rev isions 1 an d 2 of NU RE G/C R-4461 are sim ilar to those used in the initial v ersion of N UR EG/CR-4461 , p ublishe d in 1986 , w ith the addition o f a t e r m t o a c c o u n t f o r t h e f i n i t e d i me n s i o n s o f s t r u c t u r e s (s o me t i me s c a l l e d t h e "l i f e l i n e" t e r m)an d co ns id er at io n of th e v ar ia ti on o f w in d sp ee ds a lo ng a nd a cr os s th e to rn ad o fo ot pr in t. R.C. G ar so n et a l.(R ef. 6) di sc us s in d et ai l t he te rm a ss oc ia te d w it h th e fi ni te d im en si on s of s tr uc tu re s. Th e li fe li ne te rm assum es tha t a to rnado strik ing any po int on a finite struc ture ca n ca use dam ag e. The orig inal v ersion of N UR EG/CR-4461 use d a point m odel and assum ed th e nu clear p owe r plan t to be a po int struc ture. Therefore, includin g the finite dim ension s of structures increases the tornado strik e pro bability. WASH-1300 and the orig inal v ersion of this reg ulatory g uide did n ot co nsider the lifeline term and use d the o rig inal F uji ta scale.Meteorolog ical an d top og raphic cond itions, whic h v ary sig nificantly w ithin th e co ntinental U ni te d S ta te s, in fl ue nc e th e fr eq ue nc y o f oc cu rr en ce a nd in te ns it y o f to rn ad oe s. Th e N R C s ta ff has determ ined that the des ig n-basis tornado w ind s peeds for new reacto rs sho uld c orrespo nd to the exceed ance frequen cy of 10 per y ear (calc ulated as a best e stim ate), thus using the sam e ex ceedan ce!7 frequen cy as the o rig inal v ersion of this reg ulatory g uide. The results o f the analy sis ind icated that a m ax im um w in d sp ee d of 1 03 m et er s pe r se co nd (m/s) [2 30 m il es p er h ou r (m ph)] is a pp ro pr ia te for torn adoes for the ce ntral p ortion of the U nited States; a m axim um w ind s peed of 8 9 m/s (20 0 m ph)is a pp ro pr ia te f or a la rg e re g io n of th e U ni te d S ta te s al on g th e ea st c oa st , th e no rt he rn b or de r, a nd w es te rn Great Plains; and a m axim um w ind s peed of 7 2 m/s (16 0 m ph) is app ropriate for the w estern United State s. These g eog raphic wind spe ed re g ions are d efined by ob serv ed to rnado occ urrences w ithin th e tw o-deg ree la ti tu de a nd lo ng it ud e bo xe s in th e co nt ig uo us U ni te d S ta te s. F ig ur e 1 sh ow s th e th re e to rn ad o in te ns it y reg ions for the con tig uous U nited States at the 10 per y ear p robab ility lev el, in w hich the ab scissa!7 is th e lo ng it ud e (d eg re es w es t) a nd th e or di na te is th e la ti tu de (de g re es n or th).

Rev. 1 of RG 1.76, Pa g e 4 Fig ure 1. Tornado intensity reg ions for the con tig uous U nited States for ex ceedan ce p robab ilities of 10 per y ear-7 Tornado Ch aract eristic sTornadoes can be c haracteriz ed b y a m utually con sistent s et of param eters, includin g m axim um to ta l w in d sp ee d; r ad iu s of m ax im um ta ng en ti al (ro ta ti on al) w in d sp ee d; to rn ad o ta ng en ti al , v er ti ca l, radial, and translationa l w ind s peeds; and asso ciated atm osph eric pre ssure chang es w ithin th e co re.To estim ate the press ure d rop and rate of pressure dro p as sociated w ith the desig n-basis tornado , this reg ulatory g uide m odels the to rnado as a sing le R ank ine co m bined v ortex, as in the orig inal v ersion of R eg ul at or y G ui de 1.76. A s in g le R an k in e co m bi ne d v or te x is a s im pl e m od el p os se ss in g o nl y a zi mut ha l vel oc i t y. T he wi nd vel oc i t i e s an d p r e s s ur e s ar e as s ume d n ot to var y wi t h t he he i ght ab ove the g round. Therefore, the flo w field is two-dim ension al. The flow field of a Ran k ine co m bined v ortex m is equ iv alent to that of a solid rotating bo dy w ithin th e co re of radius R. Outs ide th e co re, the ro tational speed falls o ff as 1/r w here r is th e dista nce from the center of the v ortex. That is to say , th e rotatio nal R speed V is g iv en b y the follow ing equ ations: (1a)(1b)Rm mI n the se eq uations , V is the m axim um rotation al spe ed, occurrin g at ra dius r = R. I n ad dition, T the R ank ine co m bined v ortex m ov es w ith the translationa l spee d V of the to rnado.

Rev. 1 of RG 1.76, Pa g e 5The pressu re dro p from a norm al atm osph eric pre ssure to the cen ter of the R ank ine co m bined v ortex is com puted by balan cing the pressure g radient and the ce ntrifug al force (cy clostroph ic bala nce)and integ rating from infinity to the ce nter o f the v ortex. The follow ing equ ation describe s this relatio nship: Rm (2)

)p = D V, w here D is th e ai r de ns it y , ta k en a s 1.22 6 k g/m (0.07 65 4 lb m/f t)2 33The follow ing equ ation describe s the m axim um rate of p ressure drop: m ax T m (3)

(dp/d t) = (V/R) )pThe N R C s ta ff c ho se th e R an k in e co m bi ne d v or te x m od el f or it s si m pl ic it y , a s co m pa re d to the m odel dev eloped by T. F uji ta (R ef. 7). Fu j ita's m odel has a torn ado with an in ner c ore a nd an a nnulu s (outer core) w here the v ertical m otions are co ncentrate d. I n the ann ulus betw een the in ner c ore rad ius and the o uter co re radiu s, suction v ortices fo rm in strong torna does and rotate a round the center of the pare nt torn ado.mI n the Fu j ita m odel, the tornado radiu s R is larg er than the 45.7 m eters (1 50 feet) assu m ed in the orig inal v ersion of R eg ulatory G uide 1.7 6. I n fac t, th e torn ado radius of m axim um rotation al wind spe ed fo r a 103-m/s (23 0-m ph) tornado is 1 23 m eters (4 04 feet). H owe v er, the m axim um rotation al wind spe eds of the suc tion v ortices o ccur at a radius of 2 9 m eters (9 6 fee t). Desp ite the fact tha t th e pr es su re d ro p as so ci at ed w it h a su ct io n v or te x (i.e., th e pr es su re d ro p fr om a m bi en t p re ss ur e to the cen ter of the su ction v ortex) is less than that fo r the parent tornado , th e m axim um rate of p ressure drop is g reater b ecause the m axim um tim e rate of ch ang e of pressure is in v ersely pro portion al to the R ank ine com bined v ortex radius and is directly pro portion al to the tran slational speed of the R ank ine co m bined v ortex. The radius for the suc tion v ortex is sm aller than that for the pare nt torn ado, and the m axim um translationa l spee d fo r a suction v ortex is the sum of the tran slational speed of the to rnado and the speed wi t h wh i c h t he su c t i on vor t e x r ot a t e s ar ou nd th e ce nt e r of th e pa r e nt to r na do. T o a voi d a no nc on s e r vat i ve m axim um tim e rate of ch ang e of pressure , th is reg ulatory g uide retains th e 45.7-m eter (15 0-foot) ra dius of m axim um w ind s peed for the torna do used in the orig inal v ersion of R eg ulatory G uide 1.7 6. I n ad dition, this reg ulatory g uide retains th e de finition of the torna do m axim um rotation al w ind s peed Rm T V as the d ifference betw een the m axim um torna do wind spe ed V and the translationa l spee d V. The to rn ad o tr an sl at io na l s pe ed is o ne-fi ft h of th e m ax im um to rn ad o w in d sp ee d, w hi ch is c on si st en t w it h th e to rn ad o tr an sl at io na l s pe ed s in th e or ig in al v er si on o f R eg ul at or y G ui de 1.76. F ig ur e 2 de pi ct s the tran slational and rotational (or tan g ential) w ind v elocity com pone nts o f the Ran k ine co m bined v ortex.F ig ur e 2. R an k in e co m bi ne d v or te x m od el s ho w in g th e co m po ne nt s of th e w in d v el oc it y Rev. 1 of RG 1.76, Pa g e 6 Design-Basis Tornad o Charact eristic sThe orig inal v ersion of R eg ulatory G uide 1.7 6 ch aracteriz ed to rnado es in each g eog raphical reg ion by (1) m axim um w ind s peed, (2) translationa l spee d, (3) m axim um rotation al spe ed, (4) rad ius o f m axim um rotation al spe ed, (5) pre ssure drop, and (6) rate of pressure dro p. B ecause the m odel used in this reg ulatory g uide is bas ed o n a sing le R ank ine co m bined v ortex, the sam e pa ram eters ap ply. I f a tornado m odel with suction v ortices w ere u sed, add itional p aram eters w ould be n ecessary. Table 1 sum m ariz es the des ig n-basis tornado cha racteristics u sed in this reg ulatory g uide.Table 1. D esig n-Basis Tornado Cha racteristics R egi on M ax i mum w i nd spee d m/s (mph)Trans l at i onal s peed m/s (mph)M ax i mum rot at i onal s pe ed m/s (mph)R adi us of max i mum rot at i onal s peed m (f t)P res s ure dr op m b (p si)R at e of pr es s ur e dr op m b/s (p si/s)I103 (230)21 (46)82 (184)45.7 (150)83 (1.2)37 (0.5)I I89 (200)18 (40)72 (160)45.7 (150)63 (0.9)25 (0.4)I I I72 (160)14 (32)57 (128)45.7 (150)40 (0.6)13 (0.2)Tornado-Gener ated Missile Charac ter isticsTo ensure the safety of nuclear pow er plan ts in the ev ent o f a tornado strik e, NR C reg ulations re qu ir e th at n uc le ar p ow er p la nt d es ig ns c on si de r th e im pa ct o f to rn ad o-g en er at ed m is si le s (i.e., o bjec ts m ov ing un der th e actio n o f aerod y nam ic force s ind uced by the tornado w ind), in ad dition to the direct ac ti on o f th e to rn ad o w in d an d th e m ov in g a m bi en t p re ss ur e fi el d. W in d v el oc it ie s in e xc es s of 3 4 m/s (75 m ph) are ca pable of g enerating m issiles from ob j ects ly ing w ithin th e pa th of the to rnado w ind and from the debris of n earby dam ag ed s tructures.

The tw o ba si c ap pr oa ch es u se d to c ha ra ct er iz e to rn ad o-g en er at ed m is si le s ar e (1) a st an da rd s pe c t r um of to r na do m i s s i l e s , a nd (2) a p r ob a bi l i s t i c as s e s s men t of th e to r na do ha zar d. No de f i ni t i ve g uidanc e ha s be en d ev eloped for use in ch aracteriz ing site-depen dent tornado-g enerated m issiles by haz ard p robab ility m ethods. The dam ag e to safety-related structures by torna do or o ther w ind-g enerated m issiles im plies th e oc currence of a seq uence of rando m ev ents. That ev ent se quen ce ty pically inclu des a w in d-ba se d oc cu rr en ce in th e pl an t v ic in it y in e xc es s of 3 4 m/s (75 m ph), e xi st en ce a nd a v ai la bi li ty of m issiles in the are a, inj ection of m issiles into the wind field, susp ension and flig ht of those m issiles, im pact o f the m issiles w ith safety

-related structures, and resultin g dam ag e to critical eq uipm ent. G iv en d ef en se-in-de pt h co ns id er at io ns , th e un ce rt ai nt ie s in th es e ev en ts p re cl ud e th e us e of a p ro ba bi li st ic assessm ent as the sole b asis fo r asses sing ho w well the p lant is protected ag ainst to rnado m issile da m ag e.Protectio n from a spectrum of m issiles (ran g ing from a m assiv e m issile that deform s on im pact to a r ig id p en et ra ti ng m is si le) pr ov id es a ss ur an ce th at th e ne ce ss ar y s tr uc tu re s, s y st em s, a nd c om po ne nt s w il l b e av ai la bl e to m it ig at e th e po te nt ia l e ff ec ts o f a to rn ad o on p la nt s af et y. G iv en th at th e de si g n-ba si s tornado w ind s peed has a v ery low frequ ency , to be credible, the represen tativ e m issiles m ust b e com m on item s arou nd the p lant site and m ust h av e a reasona ble p robab ility of becom ing airbo rne within the tornado w ind fie ld.

Rev. 1 of RG 1.76, Pa g e 7To ev aluate the res istance of b arriers to penetratio n an d g ross fa ilure, the to rnado m issile sp eeds m ust also be defined. Sim iu an d S canlan (Ref. 8) estim ate torn ado-g enerated m issile sp eeds for nu clear plant desig n p urpose s. They assu m ed th at m issiles start their m otion from a point located on the to rnado translation axis, at a distance do wnw ard o f the tornado cen ter equ al to the rad ius o f the m axim um circum ferential w ind s peeds. I n ad dition, they assu m ed th at the speed w ith w hich a m issile hits a targ et is equ al to the m axim um spe ed (V) th at th e sa m e m is si le w ou ld a tt ai n if it s tr ajec to ry w er e m ax unob structed by the presenc e of any ob stacle.The tornad o w ind fie ld m odel used to calc ulate th e m axim um m issile v elocities differs so m ewh at fr om th e to rn ad o w in d fi el d m od el u se d in th e ab ov e di sc us si on o f to rn ad o ch ar ac te ri st ic s to o bt ai n the to rnado press ure d rop and m axim um tim e rate of ch ang e of the p ressure. C hapter 16 of R eference 8 prov ides th e torn ado wind field m odel (whic h inc ludes a rad ial com pone nt for the to rnado w ind s peed)and the eq uations of m otion used for the m axim um m issile v elocities.

The NR C staff de v eloped a co m puter prog ram to calculate the m axim um ho riz ontal m issile sp eeds by solv ing these equ ations.De sig n-Bas is T or nado M iss ile Spe c tr umI n ac cordan ce w ith 10 C FR 50.34 , "Con tents o f A pplication s; Technical I nform ation," G DC 2, and GD C 4 stru ctures, sy stem s, and com pone nts th at are im portant to safe ty m ust b e de sig ned to w ithstand the effe cts of natural phen om ena witho ut los ing the capab ility to perform their safety fun ction. Tornado m issiles are am ong the m ost ex trem e effects of credible natural phen om ena at nu clear p owe r pl a nt si t e s. T he se l e c t e d d e s i gn-ba s i s m i s s i l e s fo r nu c l e a r po we r pl a nt s in c l ud e at le a s t (1) a mas s i ve hig h-k inetic-energ y m issile that deform s on im pact, (2) a rig id m issile that tests pe netration resistence, and (3) a sm all rig id m issile of a siz e su fficient to pass throug h an y op ening in protectiv e ba rriers. The NR C staff co nsiders a 6-inch (15.24-centim eter) S chedu le 40 steel pipe and an a utom obile to be acceptab le as the p enetrating and m assiv e m issiles, respectiv ely , fo r use in the des ig n o f nu clear p owe r plan ts. Auto m obiles are co m m on objects near the p lant site, and am ple ev idence supp orts the ir pote ntial to be lifted in a torn ado wind field. S chedu le 40 pipe is a lso co m m on aroun d p lant sites.

H owe v er, such pipe is inten ded to rep resent a rig id co m pone nt of a larg er m issile (e.

g., building deb ris or an a utom obile)that m ay be lifted in the to rnado w ind fie ld. Thus, the sta ff used the m axim um spe ed c alculated for the auto m obile m issile for the p enetrating m issile as well, rather than the sp eed calculated for a pip e. To test the config uration of o pening s in the p rotectiv e ba rriers, th e m issile sp ectrum also include s a 1-inch (2.5 4-centim eter) so lid steel sphere as a sm all rig id m issile. Sim iu an d S canlan (Ref. 8) describe the m ethods that form the bases for the cha racteristics o f these m issiles. Table 2 sum m ariz es the d esig n-basis tornado m issile sp ectrum and m axim um ho riz ontal speed s.

Rev. 1 of RG 1.76, Pa g e 8 Table 2. D esig n-Basis Tornado Missile Sp ectrum and Maxim um H oriz ontal Spee ds M i s s i l e Ty peSchedul e 40 P i peA utomo bi l eSol i d Ste el Sphere D i men s i ons 0.1 6 8 m dia x 4.5 8 m l o ng (6.62 5 i n. dia x 1 5 f t l o ng)R egi o n I and II 5 m x 2 m x 1.

3 m (1 6.4 ft x 6.6 ft x 4.3 ft)2.5 4 c m d ia (1 i n. di a)R egi o n II I 4.5 m x 1.7 m x 1.5 m (1 4.9 ft x 5.6 ft x 4.9 ft)M a ss 1 3 0 kg (287 l b)R egi o n I and II 1 8 1 0 kg (4000 l b)0.0 6 6 9 kg (0.147 l b)R egi o n II I 1 1 7 8 kg (2595 l b)D C A/m 0.0 0 4 3 m/kg 2 (0.0212 f t/l b)2 R egi o n I and II 0.0 0 7 0 m/kg 2 (0.0343 f t/l b)2 0.0 0 3 4 m/kg 2 (0.0166 f t/l b)2 R egi o n II I 0.0 0 9 5 m/kg 2 (0.0464 f t/l b)2 Mh Vm ax R egi on I 4 1 m/s (1 3 5 f t/s)4 1 m/s (1 3 5 f t/s)8 m/s (2 6 f t/s)R eg i o n II 3 4 m/s (1 1 2 f t/s)3 4 m/s (1 1 2 f t/s)7 m/s (2 3 f t/s)R eg i o n III 2 4 m/s (7 9 f t/s)2 4 m/s (7 9 f t/s)6 m/s (2 0 f t/s)The NR C consid ers the m issiles listed in Table 2 to be cap able o f strik ing in all directio ns Mh Mh w it h ho ri z on ta l v el oc it ie s of V a nd v er ti ca l v el oc it ie s eq ua l t o 67 p er ce nt o f V. Ba r r i e r de s i gn m ax m ax sh ou ld b e ev al ua te d as su m in g a n or m al im pa ct to th e su rf ac e fo r th e S ch ed ul e 40 p ip e an d au to m ob il e m issiles. The au tom obile m issile is consid ered to im pact a t all altitud es less than 30 feet (9.1 4 m eters)abov e all g rade lev els w ithin 0.5 m ile (0.8 k ilom eter) of the p lant stru ctures. Table 2 inc ludes a differe nt siz e an d w eig ht au tom obile for R eg ion I I I than for Reg ions I and I I. The heav ier auto m obile used in th e ca lc ul at io ns f or R eg io ns I a nd I I w il l h av e a lo w er k in et ic e ne rg y in R eg io n I I I. Th is e ff ec t i s Mh a co nsequ ence of the low m axim um ho riz ontal speed V o f t h e h e a vi e r a u t o mo b i l e i n t h e Re gi o n I II m ax tornado w ind fie ld.

Rev. 1 of RG 1.76, Pa g e 9 C. R EGU LAT ORY PO SITIONThe N R C s ta ff h as e st ab li sh ed th e fo ll ow in g r eg ul at or y p os it io ns f or li ce ns ee s an d ap pl ic an ts to us e in selecting the desig n-basis tornado and des ig n-basis tornado-g enerated m issiles tha t a n uclear pow er plan t sho uld b e de sig ned to w ithstand to pre v ent u ndue risk to the h ealth a nd safety of the p ublic.1.

Design-Basis Tornad o P aram ete rsNuc lear po wer plants shou ld be des ig ned to w ithstand the d esig n-basis tornado. The param eter v al ue s sp ec if ie d in Ta bl e 1 fo r th e ap pr op ri at e re g io ns id en ti fi ed in F ig ur e 1 ar e g en er al ly a cc ep ta bl e to the N RC staff for de fining the desig n-basis tornado for a nu clear p owe r plan t. I f a desig n-basis tornado propo sed for a g iv en s ite is c haracteriz ed b y less-conse rv ativ e pa ram eter v alues than the reg ional v alues i n T a bl e 1, a c ompr e he ns i ve a na l ysi s sh ou l d b e pr ovi de d t o j us t i f y th e se l e c t i on of th e le s s-c on s e r vat i ve de s i gn-ba s i s to r na do. Si t e s lo c a t e d n e a r th e gen e r a l bo un da r i e s of ad j oi ni ng r e gio ns m a y in vol ve addition al con sideration

s. The rad ius o f m axim um rotation al spe ed o f 45.7 m eters (1 50 feet) is used for all three to rnado inten sity reg ions.2.

De sig n-Bas is T or nado-G e ne r at e d M iss ile Spe c tr umThe d es ig n-ba si s to rn ad o-g en er at ed m is si le s pe ct ru m in Ta bl e 2 is g en er al ly a cc ep ta bl e to the staff for the des ig n o f nu clear p owe r plan ts.

Rev. 1 of RG 1.76, Pa g e 10 D. IMP LEM ENT ATIONThe purp ose of this section is to prov ide in form ation to ap plicants and licensees reg arding the N RC staff's plans for us ing this reg ulatory g uide. N o b ack fitting is in tended or appro v ed in co nnectio n w ith its issuanc e.Exce pt in those cases in w hich an a pplican t or licensee propo ses o r has prev iously estab lished an a cceptab le alterna tiv e m ethod for co m ply ing w ith sp ecified portion s of the N RC's reg ulations, th e N R C s ta ff w il l u se th e m et ho ds d es cr ib ed in th is g ui de to e v al ua te (1) s ub m it ta ls in c on ne ct io n w it h applicatio ns fo r con struction perm its, sta ndard plan t desig n ce rtifications, early site perm its, o perating li ce ns es , a nd c om bi ne d li ce ns es; a nd (2) s ub m it ta ls f ro m o pe ra ti ng r ea ct or li ce ns ee s w ho v ol un ta ri ly propo se to initiate sy stem m odification s that hav e a clear n exus with the su bject for w hich g uidanc e is pro v ided herein.R EG U LA TO R Y A N A LY SI S / B A C KF IT A N A LY SI SThe r eg ul at or y a na ly si s an d ba ck fi t a na ly si s fo r th is r eg ul at or y g ui de a re a v ai la bl e in D ra ft Reg ulatory G uide DG-1143 , "Desig n-Basis Tornado and Tornado Missiles for Nuc lear P owe r Plan ts"(R ef. 9). Th e N R C is su ed D G-11 43 in Jan ua ry 2 00 6 to s ol ic it p ub li c co m m en t o n th e dr af t o f th is Rev ision 1 o f R eg ulatory G uide 1.7 6.

A ll NR C r eg ula tions li st ed her ei n a re a v ai la ble e le ct ronic al ly thr oug h the El ec troni c Re adi ng Room on t he NR C's 1 public W eb si te , a t h tt p://www.n rc.go v/r ead in g-r m/d o c-c o ll ect io n s/cfr. C opie s ar e al so av ai la ble f or i nspe ct ion or copy ing f or a f ee f rom the N RC's Public D ocum ent Room a t 11555 Roc k v ill e Pike , R ock v ill e, MD; t he PDR's m ai ling addr es s is U SN RC PDR, W as hing ton, DC 20555; te le phone (301) 415-4737 or (800) 397-4209; f ax (301) 415-3548; em ai l PDR@nrc.g ov.Copi es a re a v ai la ble f or i nspe ct ion or c opy ing f or a f ee f rom the N RC's Public D ocum ent Room (PDR), w hic h is 2 located at 115 55 Rockv ille P ike, Rock ville, Mary land; the P DR's m ailing address is USNRC P DR, W ashington , DC 20555. T he PDR c an al so be re ac hed by te le phone at (301) 415-4737 or (800) 397-4209, by f ax (301) 415-3548, and by e m ai l t o PDR@nrc.g ov.Copi es a re a v ai la ble f or i nspe ct ion or c opy ing f or a f ee f rom the N RC's Public D ocum ent Room a t 11555 Roc k v ill e 3 Pike , R ock v ill e, MD; t he PDR's m ai ling a ddre ss is U SN RC PDR, W as hing ton, DC 20555; te le phone (301) 415-4737 or (800) 397-4209; f ax (301) 415-3548; e m ai l PDR@nrc.g ov. C opie s ar e al so av ai la ble a t c urr ent ra te s f rom the U.S. G ov er nm ent Printi ng O f f ic e, P.O. Box 37082, W as hing ton, DC 20402-9328, te le phone (202) 512-1800; or f rom the N at iona l T ec hnic al Inf orm at ion Se rv ic e (N T IS) a t 5285 Port Roy al Roa d, Spr ing f ie ld, Virg inia 22161, online a t http://w w w.nti s.g ov, by te le phone at (800) 553-N T IS (6847) or (703) 605-6000, or by f ax to (703) 605-6900.

This docume nt is also ava ilable electronically thro ugh th e NRC's pub lic W eb site at http://w w w.nrc.g ov/re adi ng-r m/doc-c olle ct ions/nure g s/cont ra ct/c r4461/.T his doc um ent is a v ai la ble e le ct ronic al ly a t 4http://w w w.w ind.t tu.e du/F_Sc al e/im ag es/e f sr.pdf.Cop ies m ay be purch ased f rom the A m erican Society f or Civil Engineers (A SCE), 1 80 1 A lexa nd er Be ll Drive, 5 Reston, Virgin ia 201 90 , telepho ne (80 0) 54 8-ASCE (272 3). P urchase inform ation is av ailable thro ugh th e A SCE We b si te a t http://w w w.pubs.a sc e.org/W W W dis pla y.c g i?5011559.Rev. 1 of RG 1.76, Pa g e 11 REF ERE NC ES 1.

U.S. Cod e of Fede ral R egulatio ns , Title 10 , P art 50 , "Dom estic L icensing of Prod uction and Util izat ion Faci li ti es," U.S. Nucl ear Regulat ory Com m is si on, W ash ingto n, DC.1 2.

U.S. Cod e of Fede ral R egulatio ns , Title 10 , P art 10 0, , "Reac tor S ite C riteria,"

U.S. Nuc lear Regulat ory Com m is si on, W ash ingto n, DC.1 3.

W AS H-13 00 , "T e c hn i c a l Ba s i s fo r I nt e r i m Re gio na l T or na do Cr i t e r i a ," U.S. At omi c En e r gy Com m ission, Washin g ton, DC , May 19 74.2 4.

Ram sdell, J.V., J r., NU RE G/C R-4461 , "Tornado Clim atolog y of the C ontig uous U nited States,"Revisi on 2, PNNL-1511 2, U.S. Nucl ear Regulat ory Com m is si on, W ash ingto n, DC, Febru ary 20 07.3 5.

"A Reco m m endatio n fo r an Enh anced Fu j ita Sc ale (E F-Scale)," Wind Scienc e an d E ng ineering Cen ter, Texas Tech U niv ersity , L ubbo ck , TX, June 20 04.4 6.

Garso n, R.C., e t al., "Tornado D esig n Wind s B ased on Risk ," Journ al of the S tructura l D ivision, Proc eeding s of the A meric an Society of C ivil En gineers , Vol. 10 1, No. 9, pp. 1 883-1897 , Septem ber 1 975.5 Copi es a re a v ai la ble f or i nspe ct ion or c opy ing f or a f ee f rom the N RC's Public D ocum ent Room (PDR), w hic h is 6 located at 115 55 Rockv ille P ike, Rock ville, Mary land , the P DR's m ailing address is USNRC P DR, W ashington , DC 20555. T he PDR c an al so be re ac hed by te le phone at (301) 415-4737 or (800) 397-4209, by f ax a t (301) 415-3548, and by e m ai l t o PDR@nrc.g ov. T his do cum ent is also av ailable thro ugh th e NRC's A gency w ide Docume nts A cce ss and Ma nag em ent Sy st em (A DA MS) a t h t t p://www.n r c.go v/r ea d i n g-r m/a d ams.h t ml, unde r A cc es si on #ML 052650410.

Copi es m ay be purc has ed f rom the publi she r, John W ile y & Sons , 111 R iv er Str ee t, Hobok en, N J 07030-5774, 7 te le phone (201) 748-6000.

Purc has e inf orm at ion i s av ai la ble thr oug h the publi she r's W eb si te at h t t p://www.wi l ey.co m/W i l eyC D A/Wi l eyTi t l e/p r o d u ct C d-0 4 7 1 1 2 1 5 7 6.h t ml.Dr af t R eg ula tory G uide D G-1143 i s av ai la ble e le ct ronic al ly unde r A cc es si on #ML 053140225 in the N RC's 8 A g enc y w ide D ocum ent s A cc es s and Ma nag em ent Sy st em (A DA MS) a t ht tp://w w w.nrc.g ov/re adi ng-r m/a dam s.htm l. Copi es a re a ls o a v ai la ble f or i nspe ct ion or c opy ing f or a f ee f rom the N RC's Public D ocum ent Room (PDR), w hic h is located at 115 55 Rockv ille P ike, Rock ville Mary land; the P DR's m ailing address is USNRC P DR, W ashington , DC 20 55 5-0 00 1. The PDR can also be reac hed b y telepho ne at (301) 415-47 37 or (80 0) 39 7-4 20 9 by f ax at (301) 415-3548, a nd by e m ai l t o PDR@nrc.g ov.Rev. 1 of RG 1.76, Pa g e 12 7.

Fujita, T. Theodo re, "Work book of Tornadoes and Hig h Wind s for Eng ineering A pplication s,"SMRP R esearch Pape r N o. 165, Se ptem ber 1 978.6 8.

Sim iu, Em il, an d R obert H. Sc anlan, W ind E ffects on Stru ctures: Fu ndam entals and App lications to D esign , 3 Ed ition, J ohn Wiley & So ns, Hob ok en, NJ, A ug ust 1 996.rd 7 9.

Draft Reg ulatory G uide DG-1143 , "Desig n-Basis Tornado and Tornado Missiles for Nuc lear Pow er P lants," U.S. N uclear Reg ulatory C om m ission, Washin g ton, DC , January 20 06.8